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It is the big questions about the nature of our universe that create an interface between physics and philosophy: What is the nature of the vacuum, of the absolute nothing? Which processes are taking place in light, in a fraction of a single light oscillation? How are the propagation of light and the passage of time connected? Physicists from the University of Konstanz, led by Professor Guido Burkard and Professor Alfred Leitenstorfer, have made a significant contribution towards answering these questions. They successfully developed a physical model to describe the quantum states of the electromagnetic field for both light and vacuum on ultrashort timescales. Additionally, they explain how the electromagnetic field in a vacuum – so-called vacuum fluctuations – can be manipulated. These findings prove for the first time that the quantum states of the electromagnetic field for both light and vacuum are related to time. While efforts to reconcile quantum mechanics and the theory of relativity have proven to be a daunting challenge in modern theoretical physics, the researchers from Konstanz were able to create a further analogy between these two very different theories. Their research results, which were generated within the framework of the Collaborative Research Centre (CRC) 767 “Controlled Nanosystems" at the University of Konstanz, were published in the science journal Nature Physics on 1 July 2019.

Even within the absolute nothing of the vacuum, in which neither matter nor light are present, fluctuations in the electromagnetic field exist. This electromagnetic “background noise” of the universe is referred to as vacuum fluctuations. In 2015, the Konstanz physicist Professor Alfred Leitenstorfer and his research team were successful in experimentally measuring these vacuum fluctuations. His fundamental insights into the electromagnetic properties of the absolute nothing have now been further elaborated upon through the theoretical model created by Guido Burkard and his colleagues. Guido Burkard and his doctoral student Matthias Kizmann, the first author of the study, calculated the quantum states that exist in the electromagnetic field of light and vacuum. “Through our research, it is becoming increasingly apparent to us that even the vacuum – the space in which there is absolutely nothing – has an incredible amount of structure,” says Guido Burkard.

“Squeezed light”

Burkard and Kizmann focused their research on the analysis of so-called “squeezed light”. These are light impulses whose electromagnetic fluctuations were redistributed – or “squeezed”. This is how, for example, the electric noise of the field can be reduced, which in turn amplifies the magnetic noise, and vice versa. Kizmann and Burkard were thus able to determine the existence of a direct dependency between the electromagnetic field of light or vacuum and time. This demonstrates, among other things, that changes to how time passes for light can have an effect on the nature of the electromagnetic vacuum. This result provides an analogy between the field of quantum mechanics and the theory of relativity, which identifies an interplay between space and time on the basis of the speed of light.

A mathematical trick

A very useful “by-product” of the current research results is the key finding that the very complex electromagnetic field calculations on ultrashort timescales could be solved more easily in the future. The direct relationship between the electromagnetic field and time makes it possible to indirectly determine the state of the electromagnetic field via temporal factors. “Usually, one has to calculate the entire electromagnetic field. We were able to demonstrate that it is sufficient to calculate how time changes – this also allows us to understand how the electromagnetic field changes,” explains Matthias Kizmann. The described squeezed states could be used, among other things, for an improved detection of gravitational waves in the future.

Facts:

• Analysis of quantum states of light and vacuum fluctuations in the femtosecond time range.
• Research results show a relation between the electromagnetic field of light or vacuum and time.
• Original publication: Matthias Kizmann, Thiago Lucena de M. Guedes, Denis V. Seletskiy, Andrey S. Moskalenko, Alfred Leitenstorfer and Guido Burkard: Subcycle squeezing of light from a time flow perspective, Nature Physics, published 1 July 2019, DOI: 10.1038/s41567-019-0560-2, Link: https://www.nature.com/articles/s41567-019-0560-2
• Research carried out within the framework of the Collaborative Research Centre (CRC) 767 “Controlled Nanosystems" at the University of Konstanz.
• Funded by the German Research Foundation (DFG) and in the context of the Landesgraduiertenförderungsgesetz (LGFG, state law on graduate funding) Baden-Württemberg.